Have system participants reference the em entity

[sebastian-peter]

This is very much open to discussion, but here's my idea:

Rather than having a rather cumbersome UUID[] connectedAssets in EmInput that references the connected system participants, have all SystemParticipantInputs (optionally) reference the EmInput that they're connected to by id (or directly by object).
This has the additional benefit of signaling at one glance which system participant is em-controlled and which is not.

Lastly, documenation needs to be adapted.

cc @t-ober @danielfeismann